There are many known types of welding-type power supplies. Welding-type power, as used herein, refers to power suitable for electric arc welding, plasma cutting or induction heating. Welding-type systems are often used in a variety of applications and often include an auxiliary output to mimic utility power for powering tools, lights, etc. Welding-type system, as used herein, is a system that can provide welding type power, and can include control and power circuitry, wire feeders, and ancillary equipment. Utility power, as used herein, is power provided at a voltage and frequency by an electric utility.
Providing welding-type power, and designing systems to provide welding type power, provides for some unique challenges. For example, power supplies for most fields are dedicated to a single input and single output, or are rarely moved from one input to another. But, welding type systems will often be moved from one location to another, and be used with different inputs, such as single or three phase, or 115V, 230V, 460V, 575V, etc., or 50 hz or 60 hz signals, and be required to provide welding power and auxiliary power. Power supplies that are designed for a single input cannot provide a consistent output across different input voltages, and components in these power supplies that operate safely at a particular input level can be damaged when operating at an alternative input level. Also, power supplies for most fields are designed for relatively steady loads. Welding, on the other hand, is a very dynamic process and numerous variables affect output current and load, such as arc length, electrode type, shield type, air currents, dirt on the work piece, puddle size, weld orientation, operator technique, and lastly the type of welding process determined to be most suitable for the application. These variables constantly change, and lead to a constantly changing and unpredictable output current and voltage. Moreover, welding systems should provide auxiliary power at a constant and steady ac voltage, to properly mimic utility power. Finally, power supplies for many fields are designed for low-power outputs. Welding-type power supplies are high power and present many problems, such as switching losses, line losses, heat damage, inductive losses, and the creation of electromagnetic interference. Accordingly, welding-type power supply designers face many unique challenges.
Welding systems are often used in places where utility power is not available, and include an engine and generator to provide the power for conversion by the power circuitry. However, given the dynamic load of welding, it is challenging to match the power generated to the power consumed by the welding and auxiliary operations.
One prior art welding power supply that is well suited for portability and for receiving different input voltages is a multi-stage system with a preregulator to condition the input power and provide a stable bus, and an output circuit that converts or transforms the stable bus to a welding-type output. Examples of such welding-type systems are described in U.S. Pat. No. 7,049,546 (Thommes) and U.S. Pat. No. 6,987,242 (Geissler), and U.S. Patent Publication 20090230941 (Vogel), all three of which are owned by the owner of this invention, and hereby incorporate by reference. Miller® welders with the Autoline® feature include some of the features of this prior art.
FIG. 1 shows a prior art three-phase welding-type power supply consistent with U.S. Pat. Nos. 7,049,546 and 6,987,242 and U.S. Patent Publication 20090230941, and receives the three phase input Va, Vb and Vc on an input rectifier consisting of diodes 101-106. The rectified input is provided to a boost circuit 110, which boosts the input to a desired voltage (800V, e.g.) on a boosted or intermediate bus. Boost circuit 110 can include power factor correction, if desired. The boosted or intermediate bus is provided to a dc bus filter 112 (the bulk capacitance on the dc bus), and then to an isolated dc-dc converter 114. The dc-dc converter can include a converter (inverter, flyback, buck, etc), transformer and rectifier. The dc output is welding-type power. Such systems are significantly better than the prior art before them, and were the first welding-type systems to be “universal” in that they could accept nearly all available input power. They were also relatively portable and had improved power factors.
Prior art welding-type systems often provide auxiliary power outputs to power tools, etc. Auxiliary output power, as used herein includes, power provided to mimic utility power, such as 50/60 Hz, 120/240/200V, e.g., that can be used to power devices such as tools, lights, etc. U.S. Pat. No. 6,987,242 describes system where auxiliary power is derived using an inverter that creates a 575V signal that is stepped down by an isolation transformer to an aux power signal. While such a system is light weight and efficient compared to earlier systems, it includes an isolation transformer which increases weight and cost.
Accordingly, a welding-type system that maintains the advantages of prior art portable, universal input systems, but also avoids some of the deficiencies of the prior art is desired.